I. Field of the Invention
3-D printing technology has advanced into mainstream manufacturing for polymer based material systems and has caused a revolution in computer based manufacturing. Polymers based 3-D manufacturing maturation started with basic printing technology and existing polymer formulations. As it matured, the technology and polymer formulations evolved synergistically to deliver desired performance. Metals based 3-D printing is less mature but is beginning to follow a rapid growth curve. The metals printing technologies have narrowed primarily to powder-bed printing systems based on electron-beam, and laser direct melt and binder-jet technologies. Due to being in the early stages of maturation, little has been done to customize alloy composition to optimize overall 3-D manufactured part performance. Of the alloys being applied, refractory alloys such as titanium are among the least mature in this respect.
II. Description of the Prior Art
Problem:
The primary cost driver for all three primary 3-D manufacturing methods for titanium parts is the cost of titanium powder. As a result, the efficient use of the titanium powder is essential to successful market expansion of that product. The powder bed printing methods utilize a build box in which the component is built up layer by layer from powder. At completion the build box is full of powder and the component produced is within the box filled with the powder. After printing, the loose powder is removed from around the part and finishing operations are performed on the part. Since only a small fraction of the powder in the build box is incorporated into the part, there is a significant incentive to reuse the excess high cost powder.
Of the three primary 3-D printing methods applied to titanium alloys, the direct melt technologies based on electron-beam and laser melting represent the majority of titanium part manufacture but the excess titanium powder suffers from oxygen pickup each cycle through the process. The most common alloy for titanium parts is Ti-6A1-4V, grade 5 with a maximum allowable oxygen content of 0.2 wt %. Consequently the manufacturers want to start with as low an oxygen content in the powder as possible to enable the maximum number of re-use cycles for the powder before the oxygen content exceeds the specification limit.
At the same time, the customers for the 3-D printed Ti-6A1-4V parts want maximum mechanical tensile strength. The typical approach to achieve high strength Ti-6A1-4V parts is to increase oxygen content close to the upper limit of the Ti-6A1-4V grade 5 specification. This of course results in the minimum number of re-use cycles since the oxygen content would quickly exceed that allowed in the specification. This creates a need for a custom Ti-6A1-4V powder alloy composition to compete with the Ti-6A1-4V grade 5 composition and achieve high strength while having an initial low oxygen content to allow the maximum number of re-use cycles.